Substrate holder, apparatus for plating, and method of plating

ABSTRACT

There is provided a substrate holder configured to hold a substrate such that the substrate is exposed to and is brought into contact with a plating solution to be plated. The substrate holder comprises a contact that comes into contact with a seed layer formed on a surface of the substrate to feed electricity; a protective electrode that is biased to a higher potential side relative to the contact or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer and that is electrically connected with the seed layer directly or via an electrical conductor; and a holder main body provided with an internal space being configured to place therein an outer circumferential portion of the substrate, the contact and the protective electrode such as to be sealed from outside of the substrate holder in a state that the substrate is held by the substrate holder and configured to store therein a liquid that covers at least part of the protective electrode and at least a contact location between the seed layer and the contact.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-106977 filed Jul. 1, 2022, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a substrate holder, an apparatus for plating, and a method of plating.

BACKGROUND ART

In electroplating, in the event of a leakage of a plating solution into a substrate holder by some problem (for example, irregularities of a substrate or deterioration of a seal), the plating solution entering inside of the substrate holder may cause corrosion and/or dissolution of a seed layer and lead to poor electrical continuity. This may reduce the uniformity of plating.

U.S. Pat. Nos. 7,727,366 (PTL 1) and 8,168,057 (PTL 2) describe techniques of pressurizing one side of a seal of a substrate with a fluid to prevent invasion of the fluid from an opposite side of the seal. Japanese Unexamined Patent Publication No. 2020-117763 (PTL 3) and Japanese Unexamined Patent Publication No. 2020-117765 (PTL 4) describe techniques of injecting a liquid into an internal space that places therein an outer circumferential portion of a substrate in a sealed manner and thereby preventing invasion of a plating solution into the internal space, so as to prevent deposition of plating on the outer circumferential portion of the substrate and a contact member.

CITATION LIST Patent Literatures

PTL1: U.S. Pat. No. 7,727,366

PTL2: U.S. Pat. No. 8,168,057

PTL 3: Japanese Unexamined Patent Publication No. 2020-117763

PTL 4: Japanese Unexamined Patent Publication No. 2020-117765

SUMMARY OF INVENTION Technical Problem

Even when measures such as the techniques described in the above patent literatures are taken, the plating solution is likely to enter the internal space, depending on the degree of irregularities of the substrate or the degree of deterioration of the seal. Any of the above patent literatures, however, has no description on an effective measure in the event of invasion of the plating solution into the internal space. In a wet contact method that plates a substrate with causing a contact of the substrate holder and a seed layer of the substrate to be locally covered with a liquid (for example, pure water), even in the case where no plating solution enters the internal space, the seed layer is likely to be corroded by the local cell action that is caused by a concentration gradient of dissolved oxygen in the liquid.

One object of the present disclosure is to provide a technique that suppresses deterioration of a seed layer of a substrate.

One object of the present disclosure is to suppress reduction of the uniformity in the thickness of a plating film even when a plating solution enters a sealed space of a substrate holder.

One object of the present disclosure is to promptly detect invasion of a plating solution into a sealed space of a substrate holder.

Solution to Problem

According to one aspect, there is provided a substrate holder configured to hold a substrate such that the substrate is exposed to and is brought into contact with a plating solution to be plated. The substrate holder comprises a contact that comes into contact with a seed layer formed on a surface of the substrate to feed electricity; a protective electrode that is biased to a higher potential side relative to the contact or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer and that is electrically connected with the seed layer directly or via an electrical conductor; and a holder main body provided with an internal space, the internal space being configured to place therein an outer circumferential portion of the substrate, the contact and the protective electrode such as to be sealed from outside of the substrate holder in a state that the substrate is held by the substrate holder and configured to store therein a liquid that covers at least part of the protective electrode and at least a contact location between the seed layer and the contact.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating the overall configuration of a plating apparatus according to one embodiment;

FIG. 2 is a plan view illustrating the overall configuration of the plating apparatus according to the embodiment;

FIG. 3 is a schematic diagram illustrating the configuration of a plating module included in the plating apparatus according to the embodiment;

FIG. 4 is a sectional view schematically illustrating closeup of part of a substrate holder according to the embodiment;

FIG. 5 is an explanatory view illustrating a flow of a control method of the plating apparatus;

FIG. 6 is an explanatory view illustrating the flow of the control method of the plating apparatus;

FIG. 7 is a sectional view schematically illustrating closeup of part of the substrate holder having a protective electrode according to one example;

FIG. 8 is a plan view illustrating a second holding member of the substrate holder having the protective electrode according to one example;

FIG. 9 is a sectional view schematically illustrating closeup of part of the substrate holder having a protective electrode according to another example;

FIG. 10 is a plan view illustrating the second holding member of the substrate holder having the protective electrode according to another example;

FIG. 11 is an explanatory view illustrating the principle of preventing corrosion of a seed layer by the protective electrode;

FIG. 12 is a schematic diagram illustrating the configuration of an electrical continuity test model;

FIG. 13 is a photogram showing the configuration of the electrical continuity test model;

FIG. 14 is a photogram showing closeup of part of the electrical continuity test model;

FIG. 15 is a photogram showing a result of an electrical continuity test in a configuration with the protective electrode;

FIG. 16 is a photogram showing a result of the electrical continuity test in a configuration without the protective electrode;

FIG. 17 is a schematic diagram illustrating the configuration of a plating module included in a plating apparatus according to a second embodiment;

FIG. 18 is a diagram illustrating a configuration of biasing an insoluble or soluble protective electrode to a higher potential side relative to a contact in an internal space of a substrate holder in a vertical plating module;

FIG. 19 is a diagram illustrating a configuration of connecting a soluble protective electrode with a contact in the internal space of the substrate holder in the vertical plating module;

FIG. 20 is an explanatory view illustrating dissolution of a seed layer by a concentration of dissolved oxygen;

FIG. 21 is an explanatory view illustrating dissolution of a seed layer by shunt current; and

FIG. 22 is an equivalent circuit diagram illustrating the shunt current.

DESCRIPTION OF EMBODIMENTS

The following describes a plating apparatus 1000 and a plating method according to one embodiment of the present disclosure with reference to drawings. The drawings are schematically illustrated, in order to facilitate understanding the features of substances. The ratio of dimensions of respective components and the like in the drawings may not be equal to those in the actual state. Cartesian coordinates X-Y-Z are illustrated in some of the drawings for the purpose of reference. In the Cartesian coordinates, a Z direction corresponds to an upward direction, and a -Z direction corresponds to a downward direction (direction where the gravity acts).

In the description hereof, the term “substrate” includes not only semiconductor substrates, glass substrates, liquid crystal substrates and printed circuit boards but magnetic recording media, magnetic recording sensors, mirrors, optical elements, micromachine elements, partially manufactured integrated circuit boards, and any other objects to be processed. The substrate may have any of various shapes including polygonal and circular shapes. The expressions such as “front face”, “rear face”, “upper face”, “lower face”, “front”, “back”, “above or upward”, “below or downward”, “left or leftward” and “right or rightward” may be used in the description hereof. These expressions indicate positions, directions, and orientations on the sheet surfaces of respective illustrated drawings for the convenience of explanation but may be different from actual layouts, for example, in the apparatus in use.

First Embodiment

FIG. 1 is a perspective view illustrating the overall configuration of the plating apparatus of this embodiment. FIG. 2 is a plan view illustrating the overall configuration of the plating apparatus of this embodiment. As illustrated in FIGS. 1 and 2 , a plating apparatus 1000 includes load ports 100, a transfer robot 110, aligners 120, pre-wet modules 200, pre-soak modules 300, plating modules 400, cleaning modules 500, spin rinse dryers 600, a transfer device 700, and a control module 800.

The load port 100 is a module for loading a substrate housed in a cassette, such as a FOUP, (not illustrated) to the plating apparatus 1000 and unloading the substrate from the plating apparatus 1000 to the cassette. While the four load ports 100 are arranged in the horizontal direction in this embodiment, the number of load ports 100 and arrangement of the load ports 100 are arbitrary. The transfer robot 110 is a robot for transferring the substrate that is configured to grip or release the substrate between the load port 100, the aligner 120, the pre-wet module 200, and the spin rinse dryers 600. The transfer robot 110 and the transfer device 700 can perform delivery and receipt of the substrate via a temporary placement table (not illustrated) to grip or release the substrate between the transfer robot 110 and the transfer device 700.

The aligner 120 is a module for adjusting a position of an orientation flat, a notch, and the like of the substrate in a predetermined direction. While the two aligners 120 are disposed to be arranged in the horizontal direction in this embodiment, the number of aligners 120 and arrangement of the aligners 120 are arbitrary. The pre-wet module 200 wets a surface to be plated of the substrate before a plating process with a process liquid, such as pure water or deaerated water, to replace air inside a pattern formed on the surface of the substrate with the process liquid. The pre-wet module 200 is configured to perform a pre-wet process to facilitate supplying the plating solution to the inside of the pattern by replacing the process liquid inside the pattern with a plating solution during plating. While the two pre-wet modules 200 are disposed to be arranged in the vertical direction in this embodiment, the number of pre-wet modules 200 and arrangement of the pre-wet modules 200 are arbitrary.

For example, the pre-soak module 300 is configured to remove an oxidized film having a large electrical resistance present on, a surface of a seed layer formed on the surface to be plated of the substrate before the plating process by etching with a process liquid, such as sulfuric acid and hydrochloric acid, and perform a pre-soak process that cleans or activates a surface of a plating base layer. While the two pre-soak modules 300 are disposed to be arranged in the vertical direction in this embodiment, the number of pre-soak modules 300 and arrangement of the pre-soak modules 300 are arbitrary. The plating module 400 performs the plating process on the substrate. There are two sets of the 12 plating modules 400 arranged by three in the vertical direction and by four in the horizontal direction, and the total 24 plating modules 400 are disposed in this embodiment, but the number of plating modules 400 and arrangement of the plating modules 400 are arbitrary.

The cleaning module 500 is configured to perform a cleaning process on the substrate to remove the plating solution or the like left on the substrate after the plating process. While the two cleaning modules 500 are disposed to be arranged in the vertical direction in this embodiment, the number of cleaning modules 500 and arrangement of the cleaning modules 500 are arbitrary. The spin rinse dryer 600 is a module for rotating the substrate after the cleaning process at high speed and drying the substrate. While the two spin rinse dryers are disposed to be arranged in the vertical direction in this embodiment, the number of spin rinse dryers and arrangement of the spin rinse dryers are arbitrary. The transfer device 700 is a device for transfer the substrate between the plurality of modules inside the plating apparatus 1000. The control module 800 is configured to control the plurality of modules in the plating apparatus 1000 and can be configured of, for example, a general computer including input/output interfaces with an operator or a dedicated computer.

An example of a sequence of the plating processes by the plating apparatus 1000 will be described. First, the substrate housed in the cassette is loaded on the load port 100. Subsequently, the transfer robot 110 grips the substrate from the cassette at the load port 100 and transfers the substrate to the aligners 120. The aligner 120 adjusts the position of the orientation flat, the notch, or the like of the substrate in the predetermined direction. The transfer robot 110 grips or releases the substrate whose direction is adjusted with the aligners 120 to the pre-wet module 200.

The pre-wet module 200 performs the pre-wet process on the substrate. The transfer device 700 transfers the substrate on which the pre-wet process has been performed to the pre-soak module 300. The pre-soak module 300 performs the pre-soak process on the substrate. The transfer device 700 transfers the substrate on which the pre-soak process has been performed to the plating module 400. The plating module 400 performs the plating process on the substrate.

The transfer device 700 transfers the substrate on which the plating process has been performed to the cleaning module 500. The cleaning module 500 performs the cleaning process on the substrate. The transfer device 700 transfers the substrate on which the cleaning process has been performed to the spin rinse dryer 600. The spin rinse dryer 600 performs the drying process on the substrate. The transfer robot 110 receives the substrate from the spin rinse dryer 600 and transfers the substrate, on which the drying process is performed, to the cassette at the load port 100. Finally, the cassette housing the substrate is unloaded from the load port 100.

The configuration of the plating apparatus 1000 illustrated in FIG. 1 and FIG. 2 is only one example, and the configuration of the plating apparatus 1000 is not limited to the configuration of FIG. 1 and FIG. 2 .

(Configuration of Plating Module)

The following describes the plating module 400. The plurality of plating modules 400 included in the plating apparatus 1000 of the embodiment have similar configurations. Accordingly the description regards one plating module 400.

FIG. 3 is a schematic diagram illustrating the configuration of the plating module 400 included in the plating apparatus 100 of the embodiment. The plating apparatus 1000 and the plating module 400 according to the embodiment are face down-type, cup-type or horizontal plating apparatus and plating module. The plating module 400 in the plating apparatus 100 of the embodiment mainly includes a plating tank 10, a substrate holder 300 that is also referred to as a plating head, a rotating mechanism 40, a tilting mechanism 45, and a lift mechanism 46. The tilting mechanism 45 may, however, be omitted.

The plating tank 10 according to the embodiment is configured by a bottomed vessel having an opening on an upper side thereof. The plating tank 10 has a bottom wall and a circumferential wall extended upward from an outer periphery of this bottom wall and is open on an upper portion of this circumferential wall. The plating tank 10 stores a plating solution Ps inside thereof. According to the embodiment, the plating tank 10 has a cylindrical shape.

The plating solution Ps may be any solution including an ion of a metal element to form a plating film, and its concrete examples are not specifically limited. According to the embodiment, a copper plating process is employed as one example of a plating process, and a copper sulfate solution is used as one example of the plating solution Ps. According to the embodiment, the plating solution Ps includes a predetermined additive. The plating solution Ps is, however, not limited to this composition but may be prepared not to include any additive.

An anode 16 is placed inside of the plating tank 10. The concrete type of the anode 16 is not specifically limited, but a soluble anode or an insoluble anode may be used. According to the embodiment, an insoluble anode is used as the anode 16. The concrete type of this insoluble anode is not specifically limited, but platinum, iridium oxide and the like may be used.

An overflow tank 20 configured by a bottomed vessel is provided on an outer side of the plating tank 10. The overflow tank 20 serves to temporarily accumulate the plating solution Ps flowing over an upper edge of the plating tank 10. In one example, the plating solution Ps in the overflow tank 20 is discharged from a discharge outlet (not shown) for the overflow tank 20, is temporarily accumulated in a reservoir tank (not shown), and is returned to the plating tank 10.

A porous resistor 17 is placed above the anode 16 inside of the plating tank 10. More specifically, the resistor 17 is configured by a porous plate member having a plurality of pores (fine pores). The plating solution Ps on a lower side of the resistor 17 is allowed to pass through the resistor 17 and flow to an upper side of the resistor 17. This resistor 17 is a member provided to homogenize an electric field formed between the anode 16 and a substrate Wf. Placing such a resistor 17 in the plating tank 10 facilitates uniformization of the film thickness of a plating film (plating layer) formed on the substrate Wf. The resistor 17 is, however, not an essential component according to the embodiment, but the embodiment may be configured without the resistor 17.

The substrate holder 30 is a member configured to hold the substrate Wf serving as a cathode. More specifically, the substrate holder 30 is placed above the anode 16 (and is further above the resistor 17 according to the embodiment). The substrate holder 30 holds the substrate Wf in such a manner that a lower face Wfa of the substrate Wf is opposed to the anode 16 and the resistor 17. The lower face Wfa of the substrate Wf corresponds to a plating surface or a surface to be plated.

The substrate holder 30 according to the embodiment includes a first holding member 31, a second holding member 32, contacts 50 and a seal member 55. The first holding member 31 and the second holding member 32 may collectively be referred to as a holder main body. The substrate holder 30 holds the substrate Wf in such a manner that the substrate Wf is placed between and held by the first holding member 31 and the second holding member 32. The first holding member 31 holds an upper face of the substrate Wf. The second holding member 32 holds an outer periphery of the lower face Wfa of the substrate Wf and has an opening which the plating surface of the substrate Wf is exposed on. More specifically, the second holding member 32 according to the embodiment holds the outer periphery of the lower face Wfa of the substrate Wf via the seal member 55. In the state that the substrate holder 30 holds the substrate Wf, the seal member 55 comes into close contact with the substrate Wf to form a sealed space (internal space) 33 that protects the contacts 50 and contact areas of the substrate Wf (areas in the outer periphery of the substrate, which are brought into contact with the contacts 50) from the plating solution.

The substrate holder 30 is connected with a rotating shaft 41 of the rotating mechanism 40. The rotating mechanism 40 is a mechanism configured to rotate the substrate holder 30. A known mechanism such as a motor may be used for the rotating mechanism 40. The tilting mechanism 45 is a mechanism configured to incline the rotating mechanism 40 and the substrate holder 30. A known tilting mechanism such as a piston and a cylinder may be used for the tilting mechanism 45. The lift mechanism 46 is supported by a support shaft 47 extended in a vertical direction. The lift mechanism 46 is a mechanism configured to lift up and down the substrate holder 30, the rotating mechanism 40 and the tilting mechanism 45 in the vertical direction. A known lift mechanism such as a direct acting actuator or linear actuator may be used for the lift mechanism 46.

The contact 50 of the substrate holder 30 is connected with a negative electrode of a DC power source 90 via a wiring (for example, bus bar) in the substrate holder 30, and the anode 16 is connected with a positive electrode of the DC power source 90 via a wiring. The DC power source 90 causes a DC current or a pulse current to flow as a plating current between the substrate Wf and the anode 16 via the plating solution Ps. The DC power source 90 is a constant current-driven power supply.

In a plating process, the rotating mechanism 40 rotates the substrate holder 30 while the lift mechanism 46 moves down the substrate holder 30, so that the substrate Wf is soaked in the plating solution Ps in the plating tank 10. When the substrate Wf is soaked in the plating solution Ps, the tilting mechanism 45 may incline the substrate holder 30 as needed basis. The DC power source 90 subsequently causes electric current to flow between the anode 16 and the substrate Wf via the plating solution Ps. A plating film is accordingly formed on the lower face Wfa of the substrate Wf.

The operations of the plating module 400 are controlled by the control module 800. The control module 800 includes a microcomputer. This microcomputer includes, for example, a CPU (central processing unit) 801 serving as a processor and a storage unit 802 serving as a non-transitory storage medium. In the control module 800, the CPU 801 operates based on commands of programs stored in the storage unit 802. The control module 800 accordingly controls portions to be controlled in the plating module 400. The programs include, for example, programs of performing transfer controls of the transfer robot and the transfer device, controls of processings in the respective processing modules, control of the plating process in the plating module, and control of the cleaning process, as well as programs of detecting abnormalities or faults of respective devices. The storage medium may include a non-volatile storage medium and/or a volatile storage medium. The storage medium used herein may be, for example, any of known storage media including computer-readable memories such as a ROM, a RAM and a flash memory and disk-type storage media such as a hard disk, a CD-ROM, a DVD-ROM, and a flexible disk. The control module 800 is configured to make communication with a non-illustrated upper-level controller that comprehensively controls the plating apparatus and other relevant apparatuses and to send and receive data to and from a database included in the upper-level controller. The functions of part or the entirety of the control module 800 may be configured by hardware such as ASIC. The functions of part or the entirety of the control module 800 may be configured by a PLC, a sequencer or the like. Part or the entirety of the control module 800 may be placed inside and/or outside of a housing of the plating apparatus. Part or the entirety of the control module 800 is connected with respective parts of the plating apparatus to communicate therewith by wired communication and/or wireless communication.

(Substrate Holder)

FIG. 4 is a sectional view schematically illustrating closeup of part of the substrate holder 30 (part A1 shown in FIG. 3 ). Referring to FIG. 3 and FIG. 4 , in the substrate holder 30 according to the embodiment, the contacts 50 are placed to be brought into contact with the contact areas in the outer periphery of the lower face Wfa of the substrate Wf and feed electricity to the substrate Wf. More specifically, the contacts 50 of the embodiment are placed in the second holding member 32 of the substrate holder 30. According to the embodiment, a plurality of the contacts 50 are placed in a circumferential direction of the substrate holder 30 (more specifically, in a circumferential direction of the second holding member 32). Each of the contacts 50 has a plurality of (for example, four) plate-like electrodes called fingers. The plurality of contacts 50 are arranged at equal intervals in the circumferential direction of the substrate holder 30. The number of the plurality of contacts 50 is not specifically limited but is twelve as one example according to the embodiment. The plurality of contacts 50 are electrically connected with the DC power source 90 (shown in FIG. 3 ) to feed electricity supplied from the DC power source 90 to the substrate Wf (or more specifically, to a seed layer Sd formed on the lower face Wfa of the substrate Wf).

As shown in FIG. 3 and FIG. 4 , the plating module 400 according to the embodiment is provided with the seal member 55 to suppress the contacts 50 from being exposed to and coming into contact with the plating solution Ps in the plating tank 10. The seal member 55 includes a lip portion 55A provided to be protruded toward the substrate and to be brought into contact with the lower face Wfa of the substrate Wf. More specifically, the lip portion 55A of the seal member 55 according to the embodiment is located on an inner side of the contacts 50 (on an inner side in a radial direction of the substrate holder 30) and is placed between the second holding member 32 of the substrate holder 30 and the lower face Wfa of the substrate Wf in the state that the substrate Wf is held by the substrate holder 30. In this illustrated example, the lip portion 55A is provided in the vicinity of an inner side end in the radial direction of the seal member 55. The seal member 55 has, for example, a ring shape along the outer circumference of the substrate Wf. The seal member 55 provided in the plating module 400 effectively suppresses the contacts 50 from being exposed to and coming into contact with the plating solution Ps when the substrate Wf is soaked in the plating solution Ps.

As shown in FIG. 4 , the second holding member 32 of the substrate holder 30 includes a circumferential wall 32A and a substrate receiving portion 32B protruded inward in the radial direction in the vicinity of a lower end of the circumferential wall 32A. The seal member 55 is provided in the substrate receiving portion 32B. The second holding member 32 is a member serving to hold the seal member 55 and is thus also called a seal ring holder SRH. The second holding member 32 may be configured by assembling a plurality of members. For example, the circumferential wall 32A and the substrate receiving portion 32B may be provided as separate bodies and joined with each other. The lip portion 55A is brought into contact with the substrate Wf to form the sealed space (internal space) 33 in the substrate holder 30 as shown in FIG. 3 , so as to shield/ protect contact locations of the contacts 50 with the substrate Wf (the seed layer Sd in the contact area described below) from the plating solution Ps.

According to the embodiment, as shown in FIG. 4 , the substrate Wf is subjected to the plating process in the state that a contact portion (a leading end portion in the illustrated example) of each contact 50 that is brought into contact with the substrate Wf is covered with a liquid 60. The liquid 60 may be pure water, deaerated water or another liquid (liquid used in the pre-wet process, the pre-soak process, the cleaning process or the like). More specifically, the plating module 400 is provided with a cleaning nozzle 71 configured to spray pure water on the contacts 50 without requiring detachment of the contacts 50 from the apparatus after the plating process and with a liquid receiving tray 72 configured to receive cleaning liquid waste (as shown in FIG. 6 ). An electrical conductivity meter 74 configured to measure the electrical conductivity (conductivity) of the cleaning liquid waste is placed in the liquid receiving tray 72 and/or a cleaning liquid discharge pipe 73 configured to discharge the cleaning liquid waste, so as to determine the cleaning degree of the contacts 50 from the measured conductivity of the cleaning liquid waste. The supply of the cleaning liquid from the cleaning nozzle 71 is stopped when the conductivity becomes lower than a predetermined reference value that is determined by experiment or like. This configuration enables the contact locations of the contacts 50 with the substrate Wf (the seed layer Sd) to be covered with the liquid 60 having the conductivity controlled to be lower than the predetermined reference value. The conductivity of the liquid 60 should be adjusted to such an electrical insulating performance that causes no electricity to flow between conductive members in the internal space 33 via the liquid 60. In the case of using a protective electrode described later, however, the conductivity may be adjusted to such a degree that allows a protective current to flow between the conductive member such as the seed layer or the contact and the protective electrode. As shown in FIG. 4 , even in the case where the substrate Wf is not placed in the seal ring holder, it is preferable that the leading ends of the contacts 50 are constantly covered with the liquid 60. Even when a metal derived from the seed layer Sd adheres to the leading end of the contact in the course of repeated use of the contact, this configuration causes the leading end of the contact to be constantly biased to a lower potential side relative to the protective electrode by using the protective electrode described later. This suppresses oxidation of the metal adhering to the leading end of the contact and stabilizes the resistance of the contact over a long time period.

In the plating process, electric current is made to flow between the contacts 50 and the substrate Wf in the state that the contact locations of the contacts 50 with the substrate Wf are covered with the liquid (for example, pure water) having the conductivity of lower than the predetermined reference value. According to the embodiment, the substrate receiving portion 32B is configured to hold the liquid 60 that is used to cover the contact locations of the contacts 50 which are brought into contact with the substrate Wf. Furthermore, according to the embodiment, the seal member 55 (the lip portion 55A in the illustrated example of FIG. 4 ) serves to suppress or prevent the liquid 60 from dripping inward in the radial direction. On an outer circumferential side of the substrate receiving portion 32B, the circumferential wall 32A serves to restrict the motion of the liquid 60. It may thus be regarded that the substrate receiving portion 32B of the substrate holder 30, the seal member 55 and the circumferential wall 32A configure a container portion/ reservoir portion to store the liquid 60 therein (the circumferential wall 32A may, however, not be exposed to or come into contact with the liquid 60). Accordingly, the substrate holder 30 has the container portion/ reservoir portion to store the liquid 60 therein in the internal space 33.

One experiment performed by the applicant with regard to the configuration of the embodiment set the liquid volume of pure water supplied from the cleaning nozzle 71 to be not less than 13 mL and rotated the substrate holder 30 at least by one revolution during the supply of pure water, so as to uniformly supply pure water to the contacts 50. The liquid volume of 13 mL is determined by summing up the liquid volumes of pure water required to fully wet the contact locations of the respective fingers of the contact 50 with the substrate Wf (the seed layer Sd) with regard to the twelve contacts 50 (corresponding to the entire circumference of the substrate Wf). In other words, the liquid volume of 13 mL is the liquid volume of pure water required to fully wet the contact locations of all the contacts 50 of the substrate holder 30 with the substrate Wf. The experiment performed by the applicant has shown that the conductivity of the liquid (covering liquid) 60 of not higher than 50 μS/cm has no damage on the seed layer Sd of the substrate Wf (as shown in International Patent Application No. 2021/038404). This configuration does not require to shake off the liquid (for example, pure water) adhering to the contacts 50 after cleaning of the contacts 50 but enables the cleaning liquid having the conductivity controlled to be not higher than the predetermined reference value, to be used as the covering liquid (covering water) of the contact locations of the contacts with a next substrate that is to be processed. This configuration saves the labor of drying the contacts 50 and moreover prevents the contacts 50 and the substrate Wf in the half wet state from being subjected to the plating process.

Another experiment performed by the applicant has shown that an increase in the conductivity of the liquid 60 in a range of not higher than 1000 μS/ cm has no damage on the seed layer Sd of the substrate Wf, in the case where a protective electrode is provided for preventing corrosion of the seed layer described later. Accordingly, providing the protective electrode described later significantly loosens the control of the conductivity of the covering liquid. It has also been shown that the corrosion may proceed at a higher rate than usual in a specific substrate that has the surface of a seed layer covered with a thick oxide film by the effect of, for example, a descumming process or the like performed prior to plating, even when the conductivity is not higher than 50 μS/cm. When the contact 50 is brought into contact with the seed layer Sd, the contact 50 is pressed against the seed layer Sd by a force of not less than a certain level. This scratches off the oxide film on the surface of the seed layer and part of the seed layer and makes the surface of the metal exposed, so as to reduce the contact resistance. In the case where the surface of the seed layer is covered with a thick oxide film, however, the location of corrosion is concentrated only in the vicinity of the contact where the surface of the metal is exposed. This may be the reason why corrosion proceeds at a higher rate than usual. Even in such cases, providing the protective electrode described later effectively suppresses the corrosion.

The configuration of providing the protective electrode as described later significantly expands the allowable range of the conductivity of the liquid 60 and may thus omit the control of the conductivity of the liquid 60 using the electrical conductivity meter or the like.

Furthermore, according to the embodiment, the contact area of the substrate Wf (the area that is brought into contact with the contacts 50) that is wet by a pre-treatment such as the pre-wet process is not dried until completion of plating. This configuration suppresses or prevents disadvantages or problems described below. Drying the contact area of the substrate that is wet by the pre-treatment may dry out even inside of peripheral pattern openings, may leave bubbles inside of the pattern openings in the course of plating, and may thus cause a problem that the inside of the pattern openings is not plated. The surface of the seed layer in the half-dried contact area of the substrate may be oxidized and lead to poor electric conduction. The half-wet contact location of the seed layer of the substrate with the contact may dissolve the seed layer Sd by the local cell action and/or the shunt current (split flow via the liquid between the contact 50 and the seed layer Sd at a location other than the contact location of the seed layer Sd of the substrate Wf with the contact 50) caused by dissolved oxygen. This may cause fluctuation of power feeding and lower the in-plane uniformity in the thickness of the plating film.

(Principle of Corrosion of Seed Layer)

FIG. 20 is an explanatory view illustrating dissolution of the seed layer by the local cell action caused by dissolved oxygen. It is assumed that the plating solution is mixed into a liquid Q in the sealed space 33 (shown in FIG. 3 ) filled with the air. As shown in FIG. 20 , oxygen O₂ in the air is dissolved in the liquid Q and causes a local cell action that transfers electrons from Cu in the seed layer Sd to O₂, so as to change O₂ to OH⁻ and to change Cu to Cu²⁺ to be dissolved in the liquid Q. This results in dissolution of the seed layer Sd. This reaction may cause Cu to be dissolved from the seed layer Sd and thin down the seed layer Sd to increase an electric resistance of the seed layer Sd and cause fluctuation of power feeding. This phenomenon is ascribed to that the gas-liquid interface is near to the seed layer Sd. Corrosion of the seed layer Sd by the local cell action increases the resistance value of the seed layer Sd. This facilitates dissolution of the seed layer Sd by the shunt current described later and further accelerates dissolution of the seed layer Sd.

FIG. 21 is an explanatory view illustrating dissolution of a seed layer by shunt current. FIG. 22 is an equivalent circuit diagram illustrating the shunt current. In the drawings, I_(total) denotes a total electric current flowing in a contact; I_(cw) denotes an electric current flowing via a contact location of a seed layer Sd with the contact; I_(shunt) denotes a shunt current; R_(contact) denotes a contact resistance between the contact 50 and the seed layer Sd; R_(wafer) denotes an electric resistance of the seed layer Sd; R_(dissolution) denotes an electric resistance at a dissolution location on a seed layer side in a shunt current path; R_(deposthon) denotes an electric resistance at a deposition location on a contact side in the shunt current path; and R_(electrolyte) denotes an electric resistance of a plating solution.

In the case where the contact location between the contact 50 and the seed layer Sd is covered with a liquid Q having a high conductivity (for example, a plating solution or a liquid mixed with a plating solution) in the sealed space 33, in the state of a high electric resistance R_(wafer) of the seed layer Sd and/or a high contact resistance R_(contact) between the contact 50 and the seed layer Sd, a shunt current I_(shunt) (a split flow of the electric current I_(cw) passing through the contact location) is generated to flow from the seed layer Sd via the liquid Q to the contact 50 by the oxidation reduction reaction on the surface of the seed layer Sd and on the surface of the contact 50. The shunt current I_(shunt) is made to flow when Cu is changed Cu²⁺ on the surface of the seed layer Sd and is dissolved into the liquid Q and Cu²⁺ in the liquid Q is changed to Cu on the surface of the contact 50. Generation of the shunt current may dissolve Cu in the seed layer Sd and thin down the seed layer Sd, so as to increase the electric resistance of the seed layer Sd and cause fluctuation of power feeding. This shunt current is also generated when the resistance value of the seed layer Sd is locally increased by the local cell action described above.

As described above, covering the contact location between the contact and the seed layer with the liquid having the conductivity of not higher than 50 μS/cm effectively suppresses corrosion (dissolution) of the seed layer by the local cell action and/or the shunt current. Furthermore, using a protective electrode (described later) effectively suppresses corrosion (dissolution) of the seed layer by the local cell action and/or the shunt current even when the conductivity of the covering liquid that covers the contact location between the contact and the seed layer is increased to 1000 μS/cm.

FIG. 5 and FIG. 6 are explanatory views illustrating a flow of a control method of the plating apparatus. The following describes the control method of the plating apparatus according to the embodiment with reference to these drawings.

At step S11, in the pre-wet module 200, a substrate Wf with a seed layer Sd provided on a plating surface thereof is subjected to a pre-wet process. The pre-wet process wets the plating surface of the substrate prior to a plating process with a processing liquid Lp1, such as pure water or deaerated water, and thereby replaces the air inside of a resist pattern Rp formed on the surface of the substrate Wf with the processing liquid Lp1. The substrate Wf after the pre-wet process is wet with the processing liquid Lp1, and inside of openings of the resist pattern Rp on the surface of the substrate Wf is filled with the processing liquid Lp1 (as shown in FIG. 5 ).

At step S12, in the pre-soak module 300, the substrate Wf is subjected to a pre-soak process. The pre-soak process may, however, be omitted in some cases. The pre-soak process removes an oxide film that is located, for example, on the surface of the seed layer Sd formed on the plating surface of the substrate Wf prior to the plating process and that has a high electric resistance, by etching using a processing liquid Lp2, such as sulfuric acid or hydrochloric acid, and cleans or activates a plating base surface. After the pre-soak process, the substrate Wf may be cleaned with a processing liquid Lp3, such as pure water or deaerated water. The substrate Wf after the pre-soak process is wet with the processing liquid Lp2 (or with the processing liquid Lp3), and inside of the openings of the resist pattern Rp on the surface of the substrate Wf is filled with the processing liquid Lp2 (or with the processing liquid Lp3) (as shown in FIG. 5 ). In the description below, the processing liquids Lp1, Lp2 and Lp3 may collectively be referred to as processing liquid Lp.

At step S13, the substrate Wf transferred to the plating module 400 is attached to the substrate holder 30 that is also called plating head. In this state, as shown in FIG. 5 , the substrate Wf is wet with the processing liquid Lp (Lp1, Lp2 or Lp3). It is here assumed that a contact portion 51 of the contact 50 of the substrate holder 30 is covered with a covering liquid that is the liquid 60 supplied in a cleaning process of step S15 and/or step S17 described later. The contact portion 51 of the contact 50 denotes a portion of the contact 50 (a leading end portion of the contact 50 in this illustrated example) that is brought into contact with the seed layer Sd of the substrate Wf.

At step S14, the substrate Wf held by the substrate holder 30 is soaked into a plating solution Ps in the plating tank 10 to be processed by a plating process. At step S14 shown in FIG. 5 , the resist pattern Rp of the substrate Wf is omitted. In this state, the contact location between the contact 50 of the substrate holder 30 and the substrate Wf and part of a protective electrode (described later) are covered with the liquid 60.

At step S15, after the plating process, the substrate holder 30 is lifted up to above the liquid surface of the plating solution Ps in the plating tank 10, and the plating surface of the substrate Wf is cleaned with a cleaning liquid supplied from a cleaning liquid nozzle 61 (as shown in FIG. 6 ). In this state, the substrate holder 30 and/or the cleaning liquid nozzle 61 may be rotated to uniformly spray the cleaning liquid onto the substrate Wf. This cleaning process collects the plating solution adhering to the substrate Wf to be appropriately reused, and/or, wets the plating surface of the substrate Wf to prevent the plating surface from being dried. The cleaning liquid may be, for example, pure water, deaerated water or another liquid (liquid used in the pre-wet process, the pre-soak process, the cleaning process or the like). The cleaning liquid after being used for cleaning is collected in a liquid receiving tray 62 placed below the substrate Wf and is discharged through a liquid discharge pipe 63. An electrical conductivity meter 64 may be provided in the liquid receiving tray 62 and/or in the liquid discharge pipe 63 to measure the conductivity of the collected cleaning liquid (pure water). The collected cleaning liquid may be returned to the plating tank 10 to be reused after or without concentration adjustment. The cleaning nozzle 61 and the liquid receiving tray 62 may be configured to, for example, be moved to below the substrate holder 30 when the substrate holder 30 is lifted up and to be retreated from below the substrate holder 30 after the cleaning process.

At step S16, the substrate Wf is detached form the substrate holder 30. The detached substrate Wf is sequentially transferred to the cleaning module 500 and the spin rinse dryer 600 to be subjected to a cleaning process and a drying process and is then transferred to the cassette of the load port 100 (step S18).

At step S17, the contacts 50 and the seal member 55 of the substrate holder 30 after detachment of the substrate Wf are cleaned with a predetermined amount of the cleaning liquid supplied from the cleaning nozzle 71. In this state, the substrate holder 30 is rotated by at least one revolution to uniformly supply pure water to the contacts 50. As long as pure water is supplied at least once to the contacts 50, the cleaning nozzle 71 may be rotated or both the substrate holder 30 and the cleaning nozzle 71 may be rotated. According to the embodiment, the configuration of wetting both the substrate Wf-side and the substrate holder 30-side assures that the contact portion between the contact 50 and the seed layer Sd of the substrate Wf is covered with a sufficient amount of water. The cleaning liquid 60 may be, for example, pure water, deaerated water or another liquid (liquid used in the pre-wet process, the pre-soak process, the cleaning process or the like). The cleaning liquid 60 after being used for cleaning is collected in a liquid receiving tray 72 placed below the substrate Wf and is discharged through a liquid discharge pipe 73. An electrical conductivity meter 74 is provided in the liquid receiving tray 72 and/or in the liquid discharge pipe 73 to measure the conductivity of the collected cleaning liquid (pure water). The conductivity measured by the electrical conductivity meter 74 is given to the control module 800. The control module 800 determines whether the measured conductivity of the cleaning liquid is lower than a reference value. When the control module 800 determines that the conductivity of the cleaning liquid is not lower than the reference value, the cleaning process is continued. When the control module 800 determines that the conductivity of the cleaning liquid is lower than the reference value, on the other hand, the flow returns to step S13 to wait for a next substrate Wf transferred into the plating module 400 and attaches the next substrate Wf to the substrate holder 30.

This series of processing is repeated to sequentially process a plurality of the substates Wf by the plating process. When a first substrate Wf is processed by the plating process or when a certain time period has elapsed since extraction of the substrate Wf processed in advance by the plating process, from the plating module 400, the contact portion 51 of the contact 50 of the substrate holder 30 may be dried or may be half dried. Furthermore, when some time has elapsed since completion of cleaning, carbon dioxide included in the atmosphere may be gradually dissolved in the cleaning liquid on the substrate holder to increase the electrical conductivity to or above the reference value. In such cases, prior to the plating process of the substrate Wf, the flow performs the processing of step S17 to cover the contact portion 51 of the contact 50 of the substrate holder 30 with the liquid 60 and subsequently attaches the wet substrate Wf to the substrate holder 30 at step S13.

According to the embodiment, as shown in FIG. 6 , the liquid 60 used to cover the contact portion of the contact 50 that is brought into contact with the substrate Wf is held in the substrate receiving portion 32B. Moreover, according to the embodiment, the seal member 55 (the lip portion 55A) serves to suppress or prevent the liquid 60 from dripping inward in the radial direction. Furthermore, on the outer circumferential side of the substrate receiving portion 32B, the circumferential wall 32A serves to restrict the motion of the liquid 60. It may thus be regarded that the substrate receiving portion 32B of the substrate holder 30, the seal member 55 and the circumferential wall 32A configure a container portion/ reservoir portion to store the liquid 60 therein (the circumferential wall 32A may, however, not be exposed to or come into contact with the liquid 60). Accordingly, the sealed space (the internal space) 33 has the container portion/ reservoir portion to store the liquid 60 therein. In other words, the holder main body (the first holding member 31 and the second holding member 32) has the container portion/reservoir portion or the sealed space (internal space) 33, to store the liquid 60 therein.

(Protective Electrode)

In a configuration of plating the substrate Wf in the state that at least the contact location between the contact 50 and the seed layer Sd is soaked in the liquid in the sealed space 33 of the substrate holder 30 (in a wet contact method), it has been shown by the experiment that controlling the conductivity of the liquid (for example, pure water) to be not higher than 50 μS/cm suppresses the local cell action and generation of the shunt current and thereby suppresses or prevents corrosion of the seed layer Sd as described above. In the configuration of the embodiment, it has also been shown that providing a protective electrode (also called an anti-corrosive electrode) described later suppresses or prevents corrosion of the seed layer Sd of the substrate Wf even when the conductivity of the liquid used to cover the contacts 50 is increased in a range of not higher than 1000 μS/cm. In the wet contact method, placing a protective electrode 238A or 238B (shown in FIG. 7 or FIG. 9 ) in the vicinity of the seed layer Sd to be soaked in a liquid effectively suppresses corrosion of the seed layer Sd even in the case of a higher conductivity of the liquid (including a case where a small amount of the plating solution enters the sealed space).

(External Power Supply Type)

FIG. 7 is a sectional view schematically illustrating closeup of part of the substrate holder 30 having a protective electrode 238A according to one example. FIG. 8 is a plan view illustrating the second holding member 32 of the substrate holder 30 having the protective electrode 238A according to one example. In this illustrated example, biasing the protective electrode 238A to a higher potential side relative to the seed layer Sd causes the protective electrode 238A and the seed layer Sd to respectively serve as an anode and as a cathode and suppresses corrosion of the seed layer Sd. A configuration shown in these drawings feeds electricity to the contacts 50 via a bus bar 49 placed in the substrate holder 30.

According to the embodiment, a spacer 239 for insulation is placed between the protective electrode 238A and the contact 50. The spacer 239 is configured to provide electrical insulation between the protective electrode 238A and the contact 50. In a modified configuration that the protective electrode 238A is separated and placed away from the contact 50 with a view to assuring electrical insulation therebetween, the spacer 239 may be omitted, or any other means may be provided to assure the electrical insulation therebetween. Separation by using the spacer 239 is, however, effective to assure the electrical insulation between the protective electrode 238A and the contact 50 in a limited space that is the internal space 33 of the substrate holder 30.

(External Power Supply Type, Insoluble Protective Electrode)

The protective electrode 238A is an insoluble electrode that is made of, for example, a material having a nobler (higher) spontaneous potential (standard electrode potential) than that of the material of the seed layer Sd or that is coated with such a material. The material having the nobler spontaneous potential than that of the material of the seed layer Sd means a material that is harder to serve as an anode (i.e., that is more likely to serve as a cathode) compared with the seed layer Sd in the state that the seed layer Sd and the protective electrode 238A are soaked in the liquid 60. It is preferable that the material of the protective electrode 238A is a stable material that does not have such an excessively large oxygen overvoltage as to generate oxygen by the electrode reaction and that does not cause elution or corrosion of a material component, when the protective electrode 238A is biased to a higher potential side. The material used for the protective electrode 238A may be a material generally used for an insoluble electrode for generation of oxygen and is, for example, Pt, Pt/Ti, Pt/SUS or IrO₂/Ti.

From the standpoint of suppressing corrosion of the seed layer Sd, it is preferable to place the protective electrode 238A near to the seed layer Sd (contact area) in the outer circumferential portion (edge portion) of the substrate Wf that has a high possibility of corrosion. As shown in FIG. 8 , the protective electrode 238A is provided at a position that is substantially opposed to the entire circumference of an edge of the substrate Wf. The distance between the protective electrode 238A and the edge of the substrate Wf is preferably, for example, not longer than 10 mm. In the illustrated example of FIG. 8 , the protective electrode 238A is formed continuously over the entire circumference of the edge of the substrate Wf (the entire circumference of the substrate holder 30). According to a modification, the protective electrode 238A may be provided as separate bodies corresponding to the respective contacts 50 (each contact block). The outer circumferential portion (edge portion) of the substrate Wf is, for example, a portion of the substrate that is placed in the sealed space 33 when the substrate Wf is held by the substrate holder 30.

As shown in FIG. 7 , the protective electrode 238A is placed such that at least part of the protective electrode 238A is exposed to or comes into contact with the liquid 60 or is soaked in the liquid 60. The protective electrode 238A is connected with a positive electrode of a DC power source 236, and the contact 50 (the seed layer Sd) is connected with a negative electrode of the DC power source 236 via the bus bar 49. This configuration biases the protective electrode 238A to a higher potential side relative to the seed layer Sd and causes the protective electrode 238A and the seed layer Sd to respectively serve as an anode and as a cathode. This accordingly suppresses the oxidation reaction of Cu in the seed layer Sd and suppresses corrosion (dissolution) of the seed layer Sd. The DC power source 236 is a power supply for biasing that is driven with a constant voltage or that is driven with a constant current and is configured to apply a voltage of approximate 2 V to between the protective electrode 238A and the seed layer Sd. In one example, a dry cell of 1.5 V may be used as the DC power source 236. A stabilized power supply generally used for an electroplating apparatus and the like may also be used as the DC power source. In this case, an upper limit voltage value and an upper limit current value may be set in advance in the stabilized power supply, and the stabilized power supply may be driven with a constant voltage at the current value of not higher than the upper limit current value and may be switched over to be driven with a constant current when the current value reaches the upper limit current value. This configuration prevents the flow of an excessive electric current in the case of an abrupt increase in the conductivity of the liquid 60 due to, for example, leakage of the plating solution. It is preferable that the voltage of the protective electrode 238A relative to the seed layer Sd is sufficiently larger than a difference in spontaneous potential between the seed layer Sd and the protective electrode 238A. For example, there is a difference of approximately 0.5 V between the spontaneous potential of copper and the spontaneous potential of platinum in a 0.1% diluted solution (conductivity of approximately 1000 μS/cm) of a copper sulfate plating solution (including copper of 50 g/L, sulfuric acid of 100 g/L and chlorine of 50 mg/L). In the case where the material of the seed layer Sd is copper and the material of the protective electrode 238A is platinum, it is preferable to apply a voltage that is sufficiently larger than 0.5 V.

FIG. 11 is an explanatory view illustrating the principle of preventing corrosion of the seed layer by the protective electrode. The following describes a mechanism of the insoluble protective electrode 238A to prevent corrosion. In the liquid 60, an oxidation reaction of 2H₂O→O₂+4H⁺+4e (decomposition of water) occurs in the vicinity of the protective electrode 238A. In the liquid 60, reduction reactions of O₂+4H⁺+4e→2H₂O (production of water), 2H⁺2e→H₂ (production of hydrogen) and Cu²⁺+2e→Cu (in the case where the plating solution is mixed into the liquid 60) occur, on the other hand, in the vicinity of the seed layer Sd. By these reactions, the protective electrode 238A suppresses or prevents corrosion of the seed layer Sd.

Even when the liquid 60 has a concentration gradient of dissolved oxygen (shown in FIG. 20 ), the configuration of making the protective electrode 238A serve as the anode and the seed layer Sd serve as the cathode suppresses the oxidation reaction of Cu in the seed layer Sd and suppresses or prevents corrosion of the seed layer Sd by the local cell action. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

Even when the plating solution is mixed into the liquid 60 due to leakage of the plating solution into the internal space 33, the configuration of making the protective electrode 238A serve as the anode and the seed layer Sd serve as the cathode suppresses the oxidation reaction of Cu in the seed layer Sd and suppresses or prevents corrosion of the seed layer Sd due to the local cell action (shown in FIG. 20 ) and the shunt current (shown in FIG. 21 ). This configuration accordingly suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film. In the case where an oxide film is present on the surface of the seed layer Sd, applying a sufficiently large voltage (for example, a voltage of not lower than 4V) to between the protective electrode 238A and the contact 50 causes reduction of the oxide film to a metal. Even in the case of using a specific substrate having the surface of a seed layer covered with a thick oxide film (having a thickness of, for example, 50 nm), this configuration stabilizes the contact resistance, prevents corrosion of the seed layer from being concentrated in the vicinity of the contact and thereby further effectively suppresses corrosion of the seed layer. For example, in the case of using such a substrate, an oxide film on the surface of the seed layer may be reduced by application of a large voltage prior to a plating process or in an initial stage at a start of a plating process, and a plating process may be performed after a decrease in the applied voltage to a sufficient level for preventing corrosion of the seed layer. In the case where an oxide film is present at a leading end of the contact, this oxide film may be reduced to a metal, as in the case of the oxide film on the surface of the seed layer. This configuration is effective, for example, when a metal derived from the seed layer adheres to the leading end of the contact to be oxidized in the course of a long-time use of the contact. This operation may be performed even when there is no substrate Wf and may thus be performed during an idling time without performing a plating process. Reduction of an oxide film present at the leading end of the contact improves the contact resistance that is increased by formation of the oxide film.

(External Power Supply Type, Soluble Protective Electrode)

A material having an equivalent level of a spontaneous potential (standard electrode potential) to that of the material of the seed layer Sd may be used as the material of the protective electrode 238A. In this case, biasing the protective electrode 238A to a higher potential side relative to the seed layer Sd by the DC power source 236 causes the protective electrode 238A to be dissolved prior to the seed layer Sd and accordingly makes the protective electrode 238A serve as a sacrificial electrode (soluble electrode). The material of the protective electrode 238A may be, for example, the same material as that of the seed layer Sd. The material of the protective electrode 238A may be an electrical conductor of the same material as the metal for plating. For example, the protective electrode 238A may be an electrode made of phosphorus-containing copper, like a soluble anode. A material having a lesser noble (lower) spontaneous potential than that of the seed layer Sd may be used as the material of the protective electrode 238A. This facilitates dissolution of the protective electrode 238A and improves the function as the sacrificial electrode.

The following describes a mechanism of the soluble protective electrode 238A to prevent corrosion. As shown in FIG. 11 , in the liquid 60, an oxidation reaction of M→M^(n+)+ne (for example, Cu→Cu^(n+)+ne) occurs in the vicinity of the soluble protective electrode 238A. In the liquid 60, reduction reactions of O₂+4H⁺+4e→2H₂O (production of water), 2H⁺+2e→H₂ (production of hydrogen) and Cu^(2')+2e→Cu occur, on the other hand, in the vicinity of the seed layer Sd. The soluble protective electrode 238A is dissolved prior to Cu in the seed layer Sd in this manner. This accordingly suppresses or prevents corrosion of the seed layer Sd.

Even when the liquid 60 has a concentration gradient of dissolved oxygen (shown in FIG. 20 ), dissolution of the soluble protective electrode 238A prior to the seed layer Sd suppresses or prevents corrosion of the seed layer Sd caused by the local cell action. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction in the uniformity of the thickness of the plating film.

Even when the plating solution is mixed into the liquid 60 due to leakage of the plating solution into the internal space 33, dissolution of the soluble protective electrode 238A prior to the seed layer Sd suppresses or prevents corrosion of the seed layer Sd caused by the local cell action (shown in FIG. 20 ) and the shunt current (shown in FIG. 21 ). This configuration accordingly suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction in the uniformity of the thickness of the plating film.

(Detection of Leakage)

In either of the insoluble protective electrode 238A and the soluble protective electrode 238A, a current detector 237 may be provided in the DC power source 236 or on a wiring from the DC power source 236. In this state, the control module 800 monitors the electric current flowing between the protective electrode 238A and the contact 50 (or the bus bar 49) or an electric resistance between the protective electrode 238A and the contact 50 (or the bus bar 49). The electric current flowing between the protective electrode 238A and the contact 50 (or the bus bar 49) is equivalent to electric current flowing through the liquid 60 in the internal space 33. The electric resistance between the protective electrode 238A and the contact 50 (the bus bar 49) is equivalent to the electric resistance of the liquid 60 in the internal space 33.

Application of a DC voltage to the protective electrode 238A and detection of the electric current (the electric resistance) are controlled by the control module 800. The control module 800 obtains the electric current flowing in the protective electrode 238A (the electric current flowing through the liquid 60 in the internal space 33) from the current detector 237 and detects a leakage of the plating solution into the internal space 33, based on the obtained electric current. In place of or in addition to this configuration, the control module 800 may obtain the electric current flowing in the protective electrode 238A, calculate an electric resistance value of the liquid 60 from the voltage between the protective electrode 238A and the contact 50 (the bus bar 49) and the obtained electric current, and detect a leakage based on the calculated electric resistance value.

When there is no leakage of the plating solution into the internal space 33, the liquid 60 in the internal space 33 has an extremely high electric resistance. There is accordingly no electric current flowing between the protective electrode 238A and the contact 50 (the bus bar 49) or there is a significantly small anti-corrosive electric current flowing from the protective electrode 238A to the contact 50 (the bus bar 49) accompanied with the decomposition and production reactions of water and the production reaction of hydrogen, compared with the electric current flowing in the event of a leakage of the plating solution. In the event of a leakage, on the other hand, the plating solution is mixed into the liquid 60. This decreases the electric resistance of the liquid 60 and makes the electric current flow between the protective electrode 238A and the contact 50 (the bus bar 49) (or increases the electric current). This configuration enables a leakage of the plating solution into the internal space 33 to be detected by using the protective electrode 238A.

This configuration monitors the electric current (the electric resistance) between the protective electrode 238A and the contact 50 (the bus bar 49), so as to promptly detect any leakage of the plating solution into the internal space 33. Accordingly, even in the event of a leakage of the plating solution, this configuration enables a leakage of the plating solution to be detected promptly by using the protective electrode 238A and thereby enables an abnormality or a failure of the substrate holder 30 and a replacement timing of the seal to be detected promptly. Even in the event of a leakage of such an amount of the plating solution that is likely to corrode the seed layer Sd, the protective electrode 238A suppresses dissolution of Cu and thereby suppresses or prevents corrosion of the seed layer Sd as described above. This configuration accordingly enables a leakage of the plating solution to be detected promptly and suppresses or prevents reduction of the uniformity in the thickness of the plating film. According to a modification, the protective electrode 238A may be divided into a plurality of separate bodies corresponding to the respective contacts 50. The separate bodies may respectively be connected with individual DC power sources 236 and individual current detectors 237 to apply a DC voltage and detect a leakage of the plating solution. This modified configuration allows a location where a leakage of the plating solution occurs to be roughly identified and individually controls the anti-corrosive electric current flowing in each of the contact 50. Even in the event of a leakage of the plating solution, this more effectively suppresses corrosion of the seed layer Sd.

The configuration illustrated in FIG. 7 applies a DC voltage to between the protective electrode 238A and the contact 50 (the bus bar 49) by the DC power source 236 and detects a DC current by the current detector 237. A modified configuration may use an AC power source in place of the DC power source 236 and may cause a current detector to monitor an AC current or impedance between the protective electrode 238A and the contact 50 (the bus bar 49) and detect a leakage.

According to another modification, the current detector 237 (detection of a leakage) may be omitted, and the protective electrode 238A may be used only as an electrode for preventing corrosion of the seed layer.

(Direct Connection Type, Soluble Protective Electrode)

FIG. 9 is a sectional view schematically illustrating closeup of part of the substrate holder 30 having a protective electrode 238B according to another example. FIG. 10 is a plan view illustrating the second holding member 32 of the substrate holder 30 having the protective electrode 238B according to another example. In this example, the protective electrode 238B used is an electrode that is made of a material more likely to serve as an anode (a material having a lesser noble (lower) spontaneous potential) than that of the material of the seed layer Sd and that serves as a sacrificial electrode. This example uses a difference between the spontaneous potential of the protective electrode 238B and the spontaneous potential of the seed layer Sd to make the protective electrode 238A serve as an anode and the seed layer Sd serve as a cathode. This suppresses an oxidation reaction of Cu in the seed layer Sd and suppresses corrosion (dissolution) of the seed layer. A configuration shown in these drawings feeds electricity to the contact 50 via a bus bar 49 placed in the substrate holder 30.

As shown in FIG. 9 , the protective electrode 238B is fixed to and is thus electrically connected with the contact 50 and is also electrically connected with the seed layer Sd via the contact 50. The protective electrode 238B is a soluble electrode made of a material having a lesser noble spontaneous potential (standard electrode potential) than that of the material of the seed layer Sd. The material having the lesser noble spontaneous potential than that of the material of the seed layer Sd means a material having the lower spontaneous potential than that of the material of the seed layer Sd and also a material that makes the protective electrode 238B more likely to serve as an anode than the seed layer Sd. When the material of the seed layer Sd is Cu, the material of the protective electrode 238B may be selected among Al, Zn, Fe and the like. Among them, Zn has the lowest spontaneous potential (approximately −1.1 V relative to Cu) in a 0.1% diluted solution (conductivity of approximately 1000 μS/cm) of a copper sulfate plating solution (including copper of 50 g/L, sulfuric acid of 100 g/L and chlorine of 50 mg/L) and has the high effect of suppressing corrosion of the seed layer. The protective electrode 238B may be electrically connected with the seed layer Sd via an electrical conductor other than the contact 50 and may also be electrically connected with the contact 50 via an electrical conductor other than the contact 50. According to a modification, the protective electrode 238B may be directly brought into contact with the seed layer Sd to be electrically connected with the seed layer Sd when the substrate Wf is held by the substrate holder 30. The arrangement that the protective electrode 238B is directly fixed to the contact 50 like this illustrated example simplifies the configuration of placing the protective electrode 238B in the sealed space 33.

From the standpoint of suppressing corrosion of the seed layer Sd, it is preferable to place the protective electrode 238B near to the seed layer Sd (contact area) in the outer circumferential portion (edge portion) of the substrate Wf that has a high possibility of corrosion. As shown in FIG. 10 , the protective electrode 238B is provided at a position that is substantially opposed to the entire circumference of an edge of the substrate Wf. The distance between the protective electrode 238B and the edge of the substrate Wf is preferably, for example, not longer than 10 mm. In the illustrated example of FIG. 10 , the protective electrode 238B is provided as separate bodies corresponding to the respective contacts 50 (each contact block). According to a modification, the protective electrode 238B may be provided continuously over the entire circumference of the edge of the substrate Wf (the entire circumference of the substrate holder 30).

As shown in FIG. 9 , the protective electrode 238B is placed such that at least part of the protective electrode 238B is exposed to or comes into contact with the liquid 60 or is soaked in the liquid 60 (for example, pure water). The protective electrode 238B has the lesser noble spontaneous potential than that of the seed layer Sd and is electrically connected with the seed layer Sd via the contact 50. The protective electrode 238B accordingly serves as a sacrificial electrode that is dissolved prior to the seed layer Sd and serves as a corrosion protection electrode (anti-corrosive electrode) for suppressing corrosion of the seed layer Sd.

A mechanism of preventing corrosion by using the protective electrode 238B having the lesser noble spontaneous potential than that of the seed layer Sd is equivalent to the mechanism shown in FIG. 11 with omission of the DC power source 236 and with a short circuit of the protective electrode 238A with the contact 50. As shown in FIG. 11 , in the liquid 60, an oxidation reaction of M→Mn^(n+)+ne (for example, Al→Al³⁺+3e) occurs in the vicinity of the protective electrode 238B. The material M of the protective electrode 238B is accordingly dissolved in the liquid 60. In the liquid 60, reduction reactions of O₂+4H⁺+4e 2H₂O (production of water), 2H⁺+2e→H₂ (production of hydrogen) and Cu²⁺+2e→Cu (in the case where the plating solution is mixed into the liquid 60) occur, on the other hand, in the vicinity of the seed layer Sd. The soluble protective electrode 238B is dissolved prior to the seed layer Sd in this manner. This accordingly suppresses or prevents corrosion of the seed layer Sd.

Even when the liquid 60 has a concentration gradient of dissolved oxygen (shown in FIG. 20 ), the soluble protective electrode 238B is dissolved prior to the seed layer Sd. This suppresses or prevents corrosion of the seed layer Sd by the local cell action. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

Even when the plating solution is mixed into the liquid 60 due to leakage of the plating solution into the internal space 33, the soluble protective electrode 238B is dissolved prior to the seed layer Sd. This suppresses or prevents corrosion of the seed layer Sd due to the local cell action (shown in FIG. 20 ) and the shunt current (shown in FIG. 21 ). Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

Using the protective electrode 238B of this illustrated example does not require an external power supply to bias the protective electrode 238B and thereby simplifies the configuration of the plating module. It is preferable to cover the surface of the protective electrode 238B with an anode bag, a barrier membrane or the like. This prevents oxides and hydroxides generated on the surface of the protective electrode 238B in the course of corrosion of the protective electrode 238B from dropping off from the surface of the electrode and contaminating inside of the substrate holder 30.

(Electrical Continuity Test Model)

FIG. 12 is a schematic diagram illustrating an electrical continuity test model used to test the effects of the protective electrode. FIG. 13 is a photogram showing the configuration of the electrical continuity test model, and FIG. 14 is a photogram showing closeup of part of the electrical continuity test model. As shown in FIG. 12 , this electrical continuity test model uses the insoluble protective electrode 238A and causes the protective electrode 238A to be biased to a higher potential side relative to the contact 50 (the seed layer Sd) by the DC power source 236. In this electrical continuity test, a Pt wire (having a diameter of 0.4 mm) was used as the protective electrode 238A. The electrical continuity test used the DC power source 90 to make an electric current corresponding to the plating current flow between the contact 50 and a portion of the seed layer Sd farther from the contact 50. More specifically, the electrical continuity test simulating the plating process was performed to make an electric current simulating the plating current flow between a contact portion of the seed layer Sd brought into contact with the contact and a portion of the seed layer Sd farther from the contact 50, in place of the plating current flowing between the seed layer Sd of the substrate Wf and the anode 16 (shown in FIG. 3 ). A blanket wafer without formation of a pattern such as a resist pattern was used as the substrate Wf. The electrical continuity test was performed with the contact portion of the seed layer Sd with the contact 50 and part of the protective electrode 238A covered with the liquid 60.

The photographs of the actual electrical continuity test model are shown in FIG. 13 and FIG. 14 . As shown in these photograms, the blanket wafer used as the substrate Wf is vertically placed and fixed between a jig 901, and one end of the substrate Wf is brought into contact with the contact 50. The contact 50 is held by a jig 902. The other end of the substrate Wf and the contact 50 are respectively connected with a positive electrode and a negative electrode of the DC power source 90. As shown in FIG. 14 , the protective electrode 238A configured by the Pt wire was placed below the contact 50, and one end of the Pt wire is folded in an L shape and drawn upward through a clearance of the contact 50. As shown in FIG. 13 , a drawn-out portion of the protective electrode 238A and the contact 50 are respectively connected with a positive electrode and a negative electrode of the DC power source 236. A clearance 903 between the jig 901 and the jig 902 is filled with the liquid 60 (pure water in this example).

For the purpose of comparison, an electrical continuity test was also performed in a configuration with omission of the protective electrode 238A from the configuration of the electrical continuity test model shown in FIG. 12 to FIG. 14 . FIG. 15 is a photogram showing a result of the electrical continuity test in the configuration with the protective electrode. FIG. 16 is a photogram showing a result of the electrical continuity test in the configuration without the protective electrode. As clearly shown in these photographs, the seed layer Sd has corrosion in the configuration without the protective electrode (shown in FIG. 16 ), whereas the configuration of providing the protective electrode 238A suppresses corrosion of the seed layer Sd (shown in FIG. 15 ).

Second Embodiment

FIG. 17 is a schematic diagram illustrating the configuration of a plating module included in a plating apparatus according to a second embodiment. The plating module of this embodiment is a vertical (also called dip-type or a panel-type) plating module configured to plate a substrate at a position in a vertical direction. As shown in FIG. 17 , the plating module 400 includes a plating tank 10 configured to store a plating solution Ps inside thereof and an anode 16 placed to be opposed to a substrate holder 30 in the plating tank 10. The anode 16 is held by an anode holder 60 and is placed inside of the plating tank 10. The substrate holder 30 is configured to hold a substrate Wf, such as a wafer, in a freely attachable and detachable manner and to soak the substrate Wf into the plating solution Ps in the plating tank 10. The anode 16 is connected with a positive electrode of a DC power source 90 via the anode holder 60, while the substrate Wf is connected with a negative electrode of the DC power source 90 via the substrate holder 30. When a voltage is applied to between the anode 16 and the substrate Wf, electric current flows in the substrate Wf to form a metal film on the surface of the substrate Wf in the presence of the plating solution. The substrate Wf may be in a circular shape, in a rectangular shape or any other polygonal shape, or in any other arbitrary shape.

The plating module 400 is further provided with an overflow tank 20 placed adjacent to the plating tank 10. The overflow tank 20 is configured such that the plating solution in the plating tank 10 flows over a side wall of the plating tank 10 into the overflow tank 20. The plating solution Ps flows over the side wall of the plating tank 10 into the overflow tank 20, flows from the overflow tank 20 to go through a circulation line 58 a and is returned to the plating tank 10. The circulation line 58 a is provided with, for example, a circulation pump 58 b, a thermostatic unit 58 c and a filter 58 d. The plating module 400 further includes a regulation plate 14 having an opening 14 a configured to regulate a potential distribution on the substrate Wf and a paddle 15 configured to stir and agitate the plating solution Ps, such as to uniformly supply a sufficient amount of metal ion to the surface of the substrate Wf during plating of the substrate Wf. The configuration described above is only one example, and the plating module 400 and the like may employ other configurations.

In the vertical plating module, the substrate Wf held by the substrate holder 30 is sequentially processed in the pre-wet module 200 and the pre-soak module 300 and is then transferred into the plating module 400. As shown in FIG. 18 , the substrate holder 30 includes a front plate 210 and a back plate 220 and is configured to hold the substrate Wf placed between the front plate 210 and the back plate 220. A sealed space (internal space) 33 is formed between the front plate 210 and the back plate 220 of the substrate holder 30 and is sealed by inner seals 215 and 225 and an outer seal 216.

As shown in FIG. 18 , the back plate 220 is provided with an introduction path 231 and a discharge path 232 arranged to connect the internal space 33 of the substrate holder 30 with outside of the substrate holder 30. The introduction path 231 and the discharge path 232 are illustrated as one component in FIG. 18 as a matter of convenience but are actually separate components. The introduction path 231 and the discharge path 232 are respectively provided with a valve 231A and a valve 232A to control passage and blockage in the respective paths. The valve 231A and the valve 232A are controlled by the control module 800. For example, introduction of the liquid into the internal space 33 of the substrate holder 30 may be performed by soaking the substrate holder 30 with the substrate Wf held thereby in a liquid (processing liquid, for example, pure water) in a processing tank in the pre-wet module 200 in a pre-wet process prior to a plating process and opening the valve 231A in the introduction path 231 to introduce pure water through the introduction path 231 into the internal space 33 of the substrate holder 30 and thereby fill the internal space 33 with pure water. In another example, introduction of the liquid into the internal space 33 of the substrate holder 30 may be performed by soaking the substrate holder 30 with the substrate Wf held thereby in a liquid in a processing tank and opening the valve 231A and the valve 232A to discharge the air and pure water from the internal space 33 simultaneously with introduction of pure water into the internal space 33 and thereby fill the internal space 33 with pure water. It is preferable that the internal space 33 is completely filled with pure water with no air being left. In some cases, however, a little amount of the air or bubbles may be allowed to be left according to a desired level of functions and advantageous effects described later. The foregoing describes the example of introducing pure water into the internal space of the substrate holder in the pre-wet module. According to a modification, pure water may be introduced into the internal space of the substrate holder in another module. A separate module may be provided to introduce a liquid such as pure water into the internal space of the substrate holder.

(External Power Supply Type, Insoluble Protective Electrode)

FIG. 18 illustrates a configuration that an insoluble protective electrode 235A is biased to a higher potential side relative to the contact 50 (the seed layer Sd) in the internal space 33 of the substrate holder 30 in the vertical plating module 400. It is assumed that the internal space 33 is filled with a liquid (for example, pure water) that is a processing liquid in, for example, the pre-wet module 200 as described above. This configuration is equivalent to application of the example using the insoluble protective electrode 238A in the embodiment shown in FIG. 7 and FIG. 8 to the vertical plating module. As described above with reference to FIG. 7 and FIG. 8 , this configuration also causes the protective electrode 235A and the seed layer Sd to respectively serve as an anode and as a cathode. This configuration suppresses the oxidation reaction of Cu in the seed layer Sd and thereby suppresses or prevents corrosion of the seed layer Sd. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

(External Power Supply Type, Soluble Protective Electrode)

In the embodiment shown in FIG. 18 , like the embodiment shown in FIG. 7 and FIG. 8 , a material having an equivalent level of spontaneous potential (standard electrode potential) to that of the material of the seed layer Sd or a material having a lower spontaneous potential (standard electrode potential) than that of the material of the seed layer Sd may be used as the material of a protective electrode 235A. In this case, a DC power source 236A may be used to bias the protective electrode 235A to a higher potential side relative to the seed layer Sd. This causes the protective electrode 235A to be dissolved prior to the seed layer Sd and to serve as a sacrificial electrode (soluble electrode). The material of the protective electrode 235A may be, for example, the same material as the material of the seed layer Sd (the same material as the metal for plating). As described above with reference to FIG. 7 and FIG. 8 , this configuration causes the soluble protective electrode 235A to be dissolved prior to the seed layer Sd and thereby suppresses or prevents corrosion of the seed layer Sd. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

Like the embodiment described above with reference to FIG. 7 and FIG. 8 , the configuration of this embodiment shown in FIG. 18 uses a current detector 237A to monitor an electric current flowing between the protective electrode 235A and the contact 50 (the bus bar 49) via the liquid 60 or an electric resistance therebetween, so as to detect a leakage of the plating solution Ps into the internal space 33. In the illustrated example of FIG. 18 , a modified configuration may not use the protective electrode 235A for detection of a leakage but use the protective electrode 235A only as an electrode for preventing corrosion of the seed layer Sd. The configuration illustrated in FIG. 18 applies a DC voltage to between the protective electrode 235A and the contact 50 (the bus bar 49) by the DC power source 236A and detects a DC current by the current detector 237A. A modified configuration may use an AC power source in place of the DC power source 236A and may cause a current detector to monitor an AC current or impedance between the protective electrode 235A and the contact 50 (the bus bar 49) and detect a leakage.

(Direct Connection Type, Soluble Protective Electrode)

FIG. 19 illustrates a configuration that a soluble protective electrode 235B is connected with the contact 50, i.e., a configuration that the protective electrode 235B is fixed to the contact 50 and is electrically connected with the seed layer Sd via the contact 50, in the internal space of the substrate holder in the vertical plating module. The protective electrode 235B may be electrically connected with the seed layer Sd via an electrical conductor other than the contact 50 and may also be electrically connected with the contact 50 via an electrical conductor other than the contact 50. According to a modified configuration, the protective electrode 235B may be directly brought into contact with the seed layer Sd to be electrically connected with the seed layer Sd when the substrate Wf is held by the substrate holder 30. This configuration is equivalent to application of the configuration of the embodiment shown in FIG. 9 and FIG. 10 to the vertical plating module. As described above with reference to FIG. 9 and FIG. 10 , this configuration causes the soluble protective electrode 235B to be dissolved prior to the seed layer Sd and thereby suppresses or prevents corrosion of the seed layer Sd. Accordingly, this configuration suppresses or prevents corrosion of the seed layer Sd and suppresses or prevents reduction of the uniformity in the thickness of the plating film.

FIG. 18 and FIG. 19 illustrate the configurations of the substrate holder 30 for one-side plating where only one face of the substrate Wf is exposed to the plating solution. The present disclosure is, however, not limited to the substrate holder for one-side plating but is applicable to a substrate holder for both-side plating, as well as the substrate holder for one-side plating where only one face of the substrate Wf is exposed.

In the configuration of this embodiment, the internal space 33 of the substrate holder 30 is filled with the liquid (for example, pure water). Compared with a configuration that the internal space 33 is hollow, this configuration decreases a pressure difference between inside and outside of the internal space 33 and suppresses or prevents a leakage of the plating solution into the internal space 33. This accordingly suppresses or prevents reduction of the uniformity in the thickness of the plating film due to a leakage of the plating solution.

In the configuration of this embodiment, the internal space 33 is filled with the liquid (for example, pure water). Even in the event of a leakage of the plating solution, this configuration limits invasion of the plating solution into the internal space 33 by only a diffused amount that is a very small amount. This configuration accordingly suppresses dissolution (corrosion) of the seed layer Sd by the local cell action and/or the shunt current caused by the concentration of dissolved oxygen. Moreover, the plating solution entering the internal space 33 is diluted with the liquid (for example, pure water). This further suppresses corrosion of the seed layer Sd. Accordingly, this suppresses or prevents reduction of the uniformity in the thickness of the plating film.

Furthermore, in the configuration of this embodiment, the internal space 33 is filled with the liquid (for example, pure water) and has a low oxygen concentration. This suppresses dissolution of the seed layer Sd by the local cell action due to dissolved oxygen. This accordingly suppresses or prevents reduction of the uniformity in the thickness of the plating film.

In the configuration of this embodiment, even in the event of a leakage of such an amount of the plating solution that is likely to cause corrosion, the protective electrode 235A or 235B suppresses or prevents dissolution of the seed layer Sd. This accordingly suppresses or prevents reduction of the uniformity in the thickness of the plating film due to a leakage of the plating solution.

Other Embodiments

(1) In the above embodiments, the resist pattern is given as an example of the pattern on the substrate. The pattern may be a via or trench pattern to form wirings, a resist or insulating film pattern to form bumps, rewiring, and electrode pads, or any pattern that defines the shape or configuration of a plating film.

(2) The liquid to be introduced into the internal space of the substrate holder may be a liquid other than water as long as the liquid does not corrode a component exposed on the internal space of the substrate holder. For example, the liquid may be a liquid free from a metal salt (a liquid having the concentration of a metal salt of lower than a predetermined concentration (for example, 5 g/L)). Available examples of such liquid include tap water, natural water, and pure water. The pure water includes, for example, deionized water (DIW), distilled water, purified water and RO water.

(3) The configuration of the substrate holder is not limited to the exemplified configurations described above. The embodiments of the present disclosure described above may be applied to any configuration of a substrate holder that has an internal space where a contact is sealed.

At least the following aspects are provided from the description of the above embodiments.

[1] According to one aspect, there is provided a substrate holder configured to hold a substrate such that the substrate is exposed to and is brought into contact with a plating solution to be plated. The substrate holder comprises a contact that comes into contact with a seed layer formed on a surface of the substrate to feed electricity; a protective electrode that is biased to a higher potential side relative to the contact or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer and that is electrically connected with the seed layer directly or via an electrical conductor; and a holder main body provided with an internal space, the internal space being configured to place therein an outer circumferential portion of the substrate, the contact and the protective electrode such as to be sealed from outside of the substrate holder in a state that the substrate is held by the substrate holder and configured to store therein a liquid that covers at least part of the protective electrode and at least a contact location between the seed layer and the contact.

The expression of the “liquid that covers at least part of the protective electrode and at least a contact location between the seed layer and the contact” includes the state that the entire protective electrode is covered with the liquid, the state that the entire seed layer placed in the internal space is covered with the liquid, the state that the entire contact is covered with the liquid, and/or the state that the entire internal space is filled with the liquid.

The configuration of this aspect causes the liquid in the vicinity of the protective electrode or the material of the protective electrode to be oxidized prior to the material of the seed layer and thereby suppresses dissolution of the material of the seed layer into the liquid. This suppresses or prevents corrosion (deterioration) of the seed layer. This configuration also suppresses the local cell action on the surface of the seed layer caused by the concentration gradient of dissolved oxygen in the liquid that covers the contact and the like and suppresses or prevents corrosion of the seed layer. Moreover, even in case where the plating solution enters the internal space of the substrate holder, this configuration suppresses or prevents corrosion of the seed layer by the local cell action and/or the shunt current. Providing the protective electrode suppresses deterioration of the seed layer and thereby suppresses or prevents reduction of the uniformity in the thickness of the plating film.

[2] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be an insoluble electrode and is biased to the higher potential side relative to the contact.

The configuration of this aspect does not require replacement of the protective electrode at regular intervals or decreases the frequency of replacement of the protective electrode and thereby facilitates maintenance of the protective electrode. This configuration also reduces the possibility that the electrode material (metal) dissolved from the protective electrode is mixed into the plating solution to contaminate the plating solution. This configuration further reduces the possibility that the oxide of the electrode material dissolved from the protective electrode deposits on the contact or the seal to contaminate the contact or the seal.

[3] According to one aspect, in the substrate holder of the above aspect, a voltage larger than a difference between the spontaneous potential of the protective electrode and the spontaneous potential of the seed layer may be applied to between the protective electrode and the seed layer.

The configuration of this aspect enables the protective electrode and the seed layer to respectively serve as an anode and as a cathode with certainty and reliably suppresses or prevents dissolution of the seed layer.

[4] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be fixed to the contact via a spacer.

The configuration of this aspect enables the protective electrode to be readily and appropriately placed in a narrow sealed space of the substrate holder.

[5] According to one aspect, in the substrate holder of the above aspect, the protective electrode may have a lower spontaneous potential than the spontaneous potential of the seed layer, may be electrically connected with the seed layer directly or via an electrical conductor and may serve as a soluble sacrificial electrode.

The configuration of this aspect does not require an external power source to bias the protective electrode and simplifies the configuration of the substrate holder and/or a plating module.

[6] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be fixed to the contact and may be electrically connected with the seed layer via the contact.

The configuration of this aspect directly fixes the protective electrode to the contact, so as to electrically connect the protective electrode with the seed layer via the contact. This simplifies the configuration for connection of the protective electrode.

[7] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be a soluble electrode and may be biased to the higher potential side relative to the contact.

The configuration of this aspect enables the protective electrode to serve as a sacrificial electrode for the seed layer by making the protective electrode of an identical material with the material of the seed layer. This configuration reduces the possibility that the plating solution is contaminated even when the metal dissolved from the protective electrode is mixed into the plating solution.

[8] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be fixed to the contact via a spacer.

The configuration of this aspect enables the protective electrode to be readily and appropriately placed in a limited narrow sealed space of the substrate holder.

[9] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be provided continuously or discretely in a location surrounding an outer circumference of the substrate, when the substrate is held by the substrate holder.

The configuration of this aspect enables the protective electrode to be placed near along the whole circumference of an outer circumferential portion (edge portion) of the substrate having a high possibility of corrosion and thereby effectively suppresses corrosion of the seed layer.

[10] According to one aspect, in the substrate holder of the above aspect, the protective electrode may be arranged circumferentially such as to have a distance from an edge of the substrate that is not longer than a predetermined distance, when the substrate is held by the substrate holder.

The configuration of this aspect places the protective electrode in the vicinity of the edge of the substrate and thus effectively protects the seed layer in the outer circumferential portion (edge portion) of the substrate having a high possibility of corrosion, from corrosion.

[11] According to one aspect, in the substrate holder of the above aspect, the liquid may comprise a liquid having a conductivity of not higher than 1000 μS/cm.

The configuration of this aspect allows the liquid that covers the contact and the like to have the conductivity up to 1000 μS/cm. In a wet contact method that plates a substrate in a state that a contact of a substrate holder is covered with a liquid, in a configuration without a protective electrode, it is known that the conductivity of the liquid is to be controlled to be not higher than 50 μS/cm. In a configuration with a protective electrode, on the other hand, the protective electrode suppresses corrosion of the seed layer. This significantly loosens the control of the conductivity of the liquid that covers the contact and the like.

[12] According to one aspect, in the substrate holder of the above aspect, the liquid may be pure water, or deaerated or inert gas-replaced pure water.

The configuration of this aspect enables pure water such as DIW generally used in an apparatus for plating to be used as the liquid that covers the contact and the like. This configuration accordingly has no need to separately provide the liquid that covers the contact and the like.

[13] According to one aspect, in the substrate holder of the above aspect, the protective electrode may serve as a detector, wherein the detector may be configured to monitor an electric current flowing between the protective electrode and the contact or a wiring having electrical continuity with the contact in a state that the liquid is introduced into the internal space, and thereby detect a leakage of the plating solution into the internal space. The “wiring having electrical continuity with the contact” is, for example, bus bar.

The configuration of this aspect monitors the electric current flowing between the protective electrode and the contact or the like, so as to detect any leakage of the plating solution. This configuration accordingly has no need to separately provide an electrode for detection of a leakage.

[14] According to one aspect, the substrate holder of the above aspect may be applied for a horizontal plating module configured to hold the substrate at a position in a horizontal direction or may be applied for a vertical plating module configured to hold the substrate at a position in a vertical direction.

The configuration of the above aspect is applicable to a substrate holder for a horizontal plating module or for a vertical plating module. This accordingly exerts the functions and the advantageous effects described above.

[15] According to one aspect, there is provided an apparatus for plating, comprising: the substrate holder described in any of the above aspects [1] to [14]; a liquid supply module configured to supply a liquid to the internal space of the substrate holder; and a plating module configured to cause the substrate held by the substrate holder to be exposed to and brought into contact with a plating solution and thereby to be plated. The liquid supply module may be configured by, for example, a cleaning nozzle or a processing module that uses the liquid (for example, a pre-wet module).

The configuration of this aspect uses the liquid supply module in the apparatus for plating to automatically supply the liquid to the internal space of the substrate holder.

[16] According to one aspect, in the apparatus for plating of the above aspect, the liquid supply module may comprise a cleaning nozzle configured to clean the internal space of the substrate holder and to replace the liquid present in the internal space.

The configuration of this aspect cleans the internal space of the substrate holder and enables the liquid to be kept in the internal space, prior to plating of each substrate. This configuration assures plating of the substrate with causing the contact and the like placed in the internal space of the substrate holder to be constantly covered with the clean liquid.

[17] According to one aspect, the apparatus for plating of the above aspect may further comprise a pre-wet module configured to process the substrate by a pre-wet process, wherein the plating module may cause the substrate in a wet state to be held by the substrate holder.

The configuration of this aspect enables the substrate in the wet state after the pre-wet process to be transferred into the plating module and to be held by the substrate holder. This configuration does not require a process of drying an edge of the substrate.

[18] According to one aspect, there is provided a method of plating a substrate. The method comprises providing a substrate holder provided with a protective electrode that is biased to a higher potential side relative to a contact, which is brought into contact with a seed layer formed on a surface of the substrate to feed electricity, or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer of the substrate and that is electrically connected with the seed layer directly or via an electrical conductor; introducing a liquid into an internal space of the substrate holder, which places therein an outer circumferential portion of the substrate such as to be sealed from outside, so as to cover at least part of the protective electrode and at least a contact location between the contact of the substrate holder and the seed layer of the substrate, with the liquid in the internal space; and plating the substrate held by the substrate holder in a state that the liquid is introduced into the internal space of the substrate holder.

Although the embodiments of the present invention have been described based on some examples, the embodiments of the invention described above are presented to facilitate understanding of the present invention, and do not limit the present invention. The present invention can be altered and improved without departing from the subject matter of the present invention, and it is needless to say that the present invention includes equivalents thereof. In addition, it is possible to arbitrarily combine or omit the embodiments and the modifications described above and it is also possible to arbitrarily combine or omit respective constituent elements described in the claims and the specification in a range where at least a part of the above-mentioned problem can be solved or a range where at least a part of the effect is exhibited.

The entire disclosures of U.S. Pat. No. 7,727,366 (PTL 1), U.S. Pat. No. 8,168,057 (PTL 2), Japanese Unexamined Patent Publication No. 2020-117763 (PTL 3) and Japanese Unexamined Patent Publication No. 2020-117765 (PTL 4) including the specifications, claims, drawings and abstracts are incorporated herein by reference in their entireties.

The entire disclosures of International Patent Application No. 2021/038404 and International Patent Application No. 2021/000460 including the specifications, claims, drawings and abstracts are incorporated herein by reference in their entireties.

REFERENCE SIGNS LIST

-   -   10 plating tank     -   20 overflow tank     -   14 regulation plate     -   15 paddle     -   16 anode     -   17 resistor     -   30 substrate holder     -   31 first holding member     -   32 second holding member     -   33 sealed space (internal space)     -   40 rotating mechanism     -   41 rotating shaft     -   45 tilting mechanism     -   46 lift mechanism     -   47 support shaft     -   49 bus bar     -   50 contact     -   55 seal member     -   55A lip portion     -   60 cleaning liquid (pure water)     -   90 DC power source     -   215, 225 inner seals     -   216 outer seal     -   100 load port     -   110 transfer robot     -   120 aligner     -   200 pre-wet module     -   210 front plate     -   220 back plate     -   231 introduction path     -   231 A valve     -   232 discharge path     -   232 A valve     -   235A, 235B protective electrode     -   236ADC power source     -   238A, 238B protective electrode     -   300 pre-soak module     -   400 plating module     -   500 cleaning module     -   600 spin rinse dryer     -   700 transfer device     -   800 control module     -   801 CPU     -   802 storage unit     -   1000 plating apparatus     -   Wf substrate     -   Sd seed layer     -   Ps plating solution     -   Rp resist 

What is claimed is:
 1. A substrate holder configured to hold a substrate such that the substrate is exposed to and is brought into contact with a plating solution to be plated, the substrate holder comprising: a contact that comes into contact with a seed layer formed on a surface of the substrate to feed electricity; a protective electrode that is biased to a higher potential side relative to the contact or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer and that is electrically connected with the seed layer directly or via an electrical conductor; and a holder main body provided with an internal space, the internal space being configured to place therein an outer circumferential portion of the substrate, the contact and the protective electrode such as to be sealed from outside of the substrate holder in a state that the substrate is held by the substrate holder and configured to store therein a liquid that covers at least part of the protective electrode and at least a contact location between the seed layer and the contact.
 2. The substrate holder according to claim 1, wherein the protective electrode is an insoluble electrode and is biased to the higher potential side relative to the contact.
 3. The substrate holder according to claim 2, wherein a voltage larger than a difference between the spontaneous potential of the protective electrode and the spontaneous potential of the seed layer is applied to between the protective electrode and the seed layer.
 4. The substrate holder according to claim 2, wherein the protective electrode is fixed to the contact via a spacer.
 5. The substrate holder according to claim 1, wherein the protective electrode has a lower spontaneous potential than the spontaneous potential of the seed layer, is electrically connected with the seed layer directly or via an electrical conductor and serves as a soluble sacrificial electrode.
 6. The substrate holder according to claim 5, wherein the protective electrode is fixed to the contact and is electrically connected with the seed layer via the contact.
 7. The substrate holder according to claim 1, wherein the protective electrode is a soluble electrode and is biased to the higher potential side relative to the contact.
 8. The substrate holder according to claim 7, wherein the protective electrode is fixed to the contact via a spacer.
 9. The substrate holder according to claim 1, wherein the protective electrode is provided continuously or discretely in a location surrounding an outer circumference of the substrate, when the substrate is held by the substrate holder.
 10. The substrate holder according to claim 1, wherein the protective electrode is arranged circumferentially such as to have a distance from an edge of the substrate that is not longer than a predetermined distance, when the substrate is held by the substrate holder.
 11. The substrate holder according to claim 1, wherein the liquid comprises a liquid having a conductivity of not higher than 1000 μS/cm.
 12. The substrate holder according to claim 1, wherein the liquid is pure water, or deaerated or inert gas-replaced pure water.
 13. The substrate holder according to claim 1, wherein the protective electrode serves as a detector, wherein the detector is configured to monitor an electric current flowing between the protective electrode and the contact or a wiring having electrical continuity with the contact in a state that the liquid is introduced into the internal space, and thereby detect a leakage of the plating solution into the internal space.
 14. The substrate holder according to claim 1, the substrate holder being applied for a horizontal plating module configured to hold the substrate at a position in a horizontal direction or being applied for a vertical plating module configured to hold the substrate at a position in a vertical direction.
 15. An apparatus for plating, comprising: the substrate holder according to claim 1; a liquid supply module configured to supply a liquid to the internal space of the substrate holder; and a plating module configured to cause the substrate held by the substrate holder to be exposed to and brought into contact with a plating solution and thereby to be plated.
 16. The apparatus for plating according to claim 15, wherein the liquid supply module comprises a cleaning nozzle configured to clean the internal space of the substrate holder and to replace the liquid present in the internal space.
 17. The apparatus for plating according to claim 15, further comprising: a pre-wet module configured to process the substrate by a pre-wet process, wherein the plating module causes the substrate in a wet state to be held by the substrate holder.
 18. A method of plating a substrate, the method comprising: providing a substrate holder provided with a protective electrode that is biased to a higher potential side relative to a contact which is brought into contact with a seed layer formed on a surface of the substrate to feed electricity, or that comprises a material having a lower spontaneous potential than a spontaneous potential of the seed layer of the substrate and that is electrically connected with the seed layer directly or via an electrical conductor; introducing a liquid into an internal space of the substrate holder, which places therein an outer circumferential portion of the substrate such as to be sealed from outside, so as to cover at least part of the protective electrode and at least a contact location between the contact of the substrate holder and the seed layer of the substrate, with the liquid in the internal space; and plating the substrate held by the substrate holder in a state that the liquid is introduced into the internal space of the substrate holder. 